Wave 1/2 activity

[Vorticity0123]

While reading through the very interesting Stratosphere thread on this forum, I came onto wave 1 and 2 activity. Little can be found on the internet about those waves. What is actually meant by Wave 1 and 2 activity? 

 

The only information I could find was something about it being related to Kelvin waves? (those waves also seem to be influencing TC development)

 

http://www.knmi.nl/publications/showAbstract.php?id=720 (the full article can be found on a link on that site).

 

Can anybody help me to get a little more understanding about those phenomenos? Perhaps I can then give some minor contribution to the highly informative Stratosphere topic in the future.

Edited October 20, 2013 by Vorticity0123

[forecaster]

Height fields at a given surface are superpositions of many different waves on top of each other. You can pick out the individual waves by doing something called fourier analysis, which has applications in many different fields. 

 

Once you do that you will end up with an idea of the different contributions from waves 1, 2, 3 etc. all the way up to about 9. What does this mean?

 

The numbers are the "wavenumber". This means that in a given belt of latitude, a wave with wavenumber 1 will have one peak and one trough around the entire world. This is called wave 1. Likewise, a wave with wavenumber 2 ("Wave 2") has two peaks and two troughs as you go around the globe within this latitude belt. And so on. As you can probably see, as you increase the wavenumber, you are cramming more waves in as you go around the world. So the distance between each peak and each trough gets less. This is another way of expressing the relationship between wavenumber and wavelength. Wavenumber is essentially the inverse of wavelength.

 

Long waves are usually referred to as those with wave 4 or below (aka Rossby waves or planetary waves). It is possible for these to be stationary, even in a mean westerly flow. With wavenumber 5 and above, you get into "synoptic waves" and these usually move with the mean flow (i.e. for us usually towards the east). 

 

The paper you referenced has the same idea (in terms of wave theory, wavenumber is a consistent concept), but is talking about Kelvin Waves. These occur in the atmosphere and the ocean - probably best known in the tropical atmosphere as an eastwards moving wave of about 40 knots. Usually when meteorologists talk about wavenumber they are talking about Rossby waves.

 

Your question is definitely worth asking because I suspect that around the internet some people throw these terms around without getting a real physical understanding of the terms they're hurling around. 

[lorenzo]

Fantastic post forecaster, very useful explanation that will be of benefit to many.

[Vorticity0123]

Thank you for the very comprehensive post! This clarifies a lot. I dind't even know that there was a difference between Rossby and Kelvin waves. So if I am correct, the ridge/trough system on the midlatitudes is essentially a superposition (mixture) of different numbers of waves. Likewise, on this GFS chart: 

 

 

for example, looking at about 60S, you see a number of (more or less pronounced) ridges and throughs (2 distinct waves near southern Brazil). Are those the result superposition of several waves?

 

The funny thing is that we're dealing with Fourier series at our study right now, therefore it is very nice to immediately see some very interesting examples of the use of Fourier series!

Edited October 20, 2013 by Vorticity0123

[chionomaniac]

I agree with lorenzo, thanks forecaster for a wonderful technical description of the types of wave that we refer to. 

 

And with the help of this linked site (thanks Tony for the link) we can see the two types of wave that are responsible for SSW's. The first link is from a SSW from Jan 2010  and shows a wave 1 type SSW. As can be seen from the animation on the left there is one peak and one trough up until the moment that the vortex was overcome. We call this type of SSW a displacement SSW, because the wave activity displaces the centre of the vortex from the pole.

 

http://curriculum.pmartineau.webfactional.com/wp-content/svw_gallery/test/gif/2010_01_30.gif

 

The second animation is from the previous year and shows how a standing 2 wave pattern created a SSW late in January 2009. This type of SSW is known as a split type SSW because the waves split the vortex in two.

 

http://curriculum.pmartineau.webfactional.com/wp-content/svw_gallery/test/gif/2009_01_28.gif

 

The 2009 event was strong enough to create an immediate effect in the troposphere and the effect of the waves on the potential vorticity of the stratospheric vortex is quite pronounced and can also be viewed here.

 

http://eoimages.gsfc.nasa.gov/images/imagerecords/36000/36972/npole_gmao_200901-02.mov

 

 

Hopefully these visual aids can complement forecaster's excellent narrative above.

 

 

[forecaster]

1) So if I am correct, the ridge/trough system on the midlatitudes is essentially a superposition (mixture) of different numbers of waves. Likewise, on this GFS chart: 

 

 

2) for example, looking at about 60S, you see a number of (more or less pronounced) ridges and throughs (2 waves near southern Brazil). Are those the result superposition of several waves?

 

1) Pretty much. And fourier analysis allows you to get an idea of what the composition is. 

 

2) I always find it really difficult trying to manually visualise for a given chart what the component waves might be. It might not be possible at all....however, you can think of it in a simple way just using two different waves:Imagine in your latitude belt you have just two waves. One of them is Wave 2 and the other is Wave 7. So very distinct waves. Wave 2 is perhaps stationary, very persistent whereas Wave 7 moves in the westerly flow, and by itself would just look like a standard mid-latitude zonal pattern with lows and highs. 

 

Where the Wave 2 ridge and Wave 7 ridge are in phase, there would be "constructive interference" (from standard wave theory). The resulting ridge would therefore be more intense than under other circumstances. Likewise, where the troughs are in phase, you would probably see a deep low. In areas where the phases don't match up, you would see destructive interference. So for example, a Wave 7 ridge beneath a Wave 2 trough would perhaps result in a fairly weak area of high pressure. And a Wave 7 trough + Wave 2 ridge would probably see the resulting low pressure system not being deep or not forming a closed low at all. 

 

Apparently, in the past it used to be possible for forecasters to improve on NWP by being aware of the long wave patterns in the short term. If you know that you're under a Long Wave ridge, then you would naturally expect resulting medium wave (troughs) and shortwave (troughs) moving into your area to weaken somewhat. I suspect these days this isn't really possible in the short term (due to sophistication of modern NWP), though would be an interesting experiment. In the long term it may be a different matter, and is somewhat akin to how John Holmes approaches long range forecasts using the 500hPa anomaly charts.

[Vorticity0123]

Very many thanks for the wonderful explanation both! It seems to be not as easy as I thought it was, but this greatly improves my understanding of these phenomena! I'm really in your debt now.

Are there also charts available of the compositions of the individual waves?

 

What I really like about this forum, and especially your replies to my question, is that you have the quality and patience to make meteorology highly understandable for the lesser of us, even during difficult subjects. Once again, many thanks.

[forecaster]

Very many thanks for the wonderful explanation both! It seems to be not as easy as I thought it was, but this greatly improves my understanding of these phenomena! I'm really in your debt now.

Are there also charts available of the compositions of the individual waves?

 

What I really like about this forum, and especially your replies to my question, is that you have the quality and patience to make meteorology highly understandable for the lesser of us, even during difficult subjects. Once again, many thanks.

 

Thanks, I just hope I haven't made any mistakes!

 

I am yet to find anywhere freely available online which breaks down the compositions of the waves. An exception is the FU Berlin stratospheric page which shows you the Wave 1 and 2 amplitudes. I think the NCEP stratosphere site gives you Wave 3 also. Beyond that, I'm yet to find anything. 

[lorenzo]

Here is another useful link on Waves. Thanks to Nick Sussex for this from last Winter, when everyone was debating about shortwaves, wouldn't be Winter without a shortwave drama.

 

http://www.wxonline.info/topics/waves.html

[Vorticity0123]

Here is another useful link on Waves. Thanks to Nick Sussex for this from last Winter, when everyone was debating about shortwaves, wouldn't be Winter without a shortwave drama.

 

http://www.wxonline.info/topics/waves.html

 

Thanks for the useful link! It also contains many more basic information about other interesting meteorological examples. This is going to be a great help!

 

One last question: Are longwaves and shortwaves highly variable with height? Because sometimes, meteorologists are talking about warm High Pressure areas (meaning there is a trough on top of this high). Does this perhaps mean that the longwaves become more pronounced on greater heigts, and shortwaves more on lower heights?

Edited October 22, 2013 by Vorticity0123